Field of the Invention
This invention relates to a device, in particular, a device including a reference voltage generating circuit that generates a reference voltage used in the device.
Description of the Related Art
In various semiconductor devices such as DRAMs (Dynamic Random Access Memories), internal voltage generating circuits which generate internal voltages are used. The internal voltage generating circuit generates the internal voltage based on a reference voltage generated from a reference voltage generating circuit. In this case, the reference voltage generating circuit generates a reference voltage by a reference voltage generating circuit included therein and inputs the generated reference voltage to a differential amplifying circuit. The differential amplifying circuit generates a stable reference voltage by amplifying the differential between the input reference voltage and the output of its own circuit fed back with a predetermined gain.
However, due to variations in resistors and transistors in manufacturing processes, variations are generated also in the generated reference voltage. A circuit that finely adjusts the feedback gain in order to absorb such variations in the reference voltage is a voltage adjusting circuit.
A device, which includes a reference voltage generating circuit having a plurality of resistors connected in series to each other and a plurality of gate transistors each coupled to a corresponding one of the resistors for bypassing the resistor, is described in Japanese Patent Application Laid-open No. 2000-029552.
However, each of the gate transistors require sufficient voltage to be supplied between source and drain terminals for bypassing the resister. If sufficient voltage is not supplied to the gate transistor, the gate transistor may not be fully conductive. As a result, the gate transistor may not adequately bypass the resistor or the gate transistor may bypass the resistor, but may have an improper resistance value. As a result, the reference voltage generating circuit may not generate a reference voltage properly. Nowadays the voltage level used in a device tends to be lower than in the past, so it has become more difficult to generate a proper reference voltage.